Vortex induced vibration suppression systems and methods

ABSTRACT

A system comprising a subsea structure beneath a body of water, subject to a water current; an installation vessel floating on the body of water; a line connected to the subsea structure and the installation vessel; and one or more vortex induced vibration suppression devices connected to the line, which have been lowered from the vessel to be installed on the subsea structure.

RELATED APPLICATIONS

This application claims priority to co-pending U.S. Provisional Application 60/894,748, filed Mar. 14, 2007, and having attorney docket number TH3214. U.S. Provisional Application 60/894,748 is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention is related to vortex induced vibration suppression devices, and to systems and methods for attaching the devices to structures to reduce drag and/or vortex induced vibration (VIV).

BACKGROUND OF THE INVENTION

Whenever a bluff body in a fluid environment, such as a cylinder, is subjected to a current in the fluid, it is possible for the body to experience vortex-induced vibrations (VIV). These vibrations may be caused by oscillating hydrodynamic forces on the surface, which can cause substantial vibrations of the structure, especially if the forcing frequency is at or near a structural natural frequency.

Drilling for and/or producing hydrocarbons or the like from subterranean deposits which exist under a body of water exposes underwater drilling and production equipment to water currents and the possibility of VIV. Equipment exposed to VIV may include structures ranging from the tubes of a riser system, anchoring tendons, hoses, umbilicals, and other subsea members.

There are generally two kinds of water current induced stresses to which elements of a system may be exposed. The first kind of stress as mentioned above is caused by vortex-induced alternating forces that vibrate the underwater structure in a direction perpendicular to the direction of the current. These are referred to as vortex-induced vibrations (VIV). When water flows past the structure, vortices are alternately shed from each side of the structure. This produces a fluctuating force on the structure transverse to the current. These vibrations can, depending on the stiffness and the strength of the structure and any welds, lead to unacceptably short fatigue lives. The second type of stress is caused by drag forces which push the structure in the direction of the current due to the structure's resistance to fluid flow. The drag forces may be amplified by vortex induced vibrations of the structure. For instance, a structure that is vibrating due to vortex shedding will disrupt the flow of water around it more so than a stationary umbilical. This results in greater energy transfer from the current to the structure, and hence more drag.

Many methods have been developed to reduce vibrations of sub sea structures. Some of these methods to reduce vibrations caused by vortex shedding from subsea structures operate by stabilization of the wake. These methods include streamlined fairings, wake splitters and flags. Streamlined or teardrop shaped, fairings that swivel around a structure have been developed that almost eliminate the shedding or vortexes. Other conventional methods to reduce vibrations caused by vortex shedding from sub sea structures operate by modifying the boundary layer of the flow around the structure to prevent the correlation of vortex shedding along the length of the structure. Examples of such methods include the use of helical strakes around a structure, or axial rod shrouds and perforated shrouds.

U.S. Pat. No. 6,695,539 discloses an apparatus and methods for remotely installing vortex-induced vibration (VIV) reduction and drag reduction devices on elongated structures in flowing fluid environments. The apparatus is a tool for transporting and installing the devices. The devices installed can include clamshell-shaped strakes, shrouds, fairings, sleeves and flotation modules. U.S. Pat. No. 6,695,539 is herein incorporated by reference in its entirety.

Referring now to FIG. 1, surface structure 102 is in body of water 100. Surface structure 102 is connected to subsurface structure 103 at seabed 108 by connector member 104, such as a tower, riser, cable, or tendon. Current 110 encounters connector member 104. To protect connector member 104 from vibration caused by current 110, fairings 114 have been installed. One or more collars (not shown) may be installed between adjacent fairings.

When VIV suppression devices are installed on subsea structures, each suppression device needs to be transported from a surface vessel to the desired installation location on the structure. One method to achieve this is to have a ROV travel to the surface and install one device at a time. Other tools have been proposed which can transport more than one device at a time on the tool. Each trip to the surface to retrieve a device increases the time and complexity of the installation.

There is a need in the art for improved systems and methods for suppressing VIV. There is a need in the art for systems and methods for suppressing VIV that do not suffer from the disadvantages of the prior art.

There is a need in the art for systems and methods for providing VIV suppression devices to structures, and for improved installation systems and methods for the VIV suppression devices. There is a need for systems and methods of installing VIV suppression devices with fewer trips required to the surface.

These and other needs will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a system comprising a subsea structure beneath a body of water, subject to a water current; an installation vessel floating on the body of water; a line connected to the subsea structure and the installation vessel; and one or more vortex induced vibration suppression devices connected to the line, which have been lowered from the vessel to be installed on the subsea structure.

In another aspect, the invention provides a method, comprising installing a subsea structure in a body of water, wherein the subsea structure is subject to one or more water currents; covering at least a portion of an outside surface of the subsea structure; connecting at least one line to the subsea structure and to a surface vessel; lowering at least one vortex induced vibration suppression device from the vessel on the line; and installing the vortex induced vibration suppression device from the line to the exterior of the subsea structure, covering at least a portion of an outside surface of the subsea structure.

Advantages of the invention may include one or more of the following:

improved systems and methods for suppressing VIV;

systems and methods for suppressing VIV that do not suffer from the disadvantages of the prior art;

systems and methods for providing VIV suppression devices to structures, and for improved installation systems and methods for the VIV suppression devices; and/or

systems and methods of installing VIV suppression devices with fewer trips required to the surface.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a structure subject to a current.

FIGS. 2 a-2 e illustrate a system to install suppression devices on an underwater structure.

FIGS. 3 a-3 b illustrate a fairing system being installed around a structure.

DETAILED DESCRIPTION

Referring now to FIG. 2 a, system 200 is illustrated. System 200 includes surface structure 202 near the surface of the water, which is attached to connector member 204. Connector member 204 is also connected to subsurface structure 203 near seafloor 208. Exterior to connector member 204 near seafloor 208, collar 220 has been installed. Vessel 222 is also near the surface of the water, which is connected to collar 220 by one or more lines 224. Instead of collar 220, lines 224 can be connected to structure 202 by any suitable method, such as tying the line 224 near a joint of structure 202, near a flange of structure 202, welding or gluing line 224 to structure, or other suitable means as are known in the art.

Referring now to FIG. 2 b, fairings 214 have been lowered from vessel 222 towards collar 220 along line 224. Fairings 214 act to reduce drag and/or vortex induced vibration acting on connector member 204 due to current 210. Fairings 214 may be heavier than water so that they sink towards collar 220. Fairings may be attached to each other with connectors 216.

Referring now to FIG. 2 c, vessel 222 is moved towards surface structure 202 so that fairings 214 and line 224 move closer to connector member 204.

Referring now to FIG. 2 d, subsurface vessel 230 with attachment mechanism 232, for example arms, to grip fairings 214. Subsurface vessel 230 is used to install fairings 214 about connector member 204.

Referring now to FIG. 2 e, line 224, subsurface vessel 230 and vessel 222 have been removed after the completion of fairings 214 about connector member 204. Fairings 214 may be heavier than water so that they sink towards collar 220. Alternatively, fairings 214 may be lighter than water so that they float towards another collar (not shown).

Referring now to FIG. 3 a, fairing 314 is illustrated. Fairing 314 may be installed about structure 304. Fairing 314 is biased to a closed position, for example by a spring or by an elastic material. Fairing 314 includes member 316, which keeps fairing 314 from closing. Fairing 314 includes connection mechanism, for example a male member 318 a which can be received within and lock within a female member 318 b. Fairing 314 includes two line guides 320 a and 320 b. Line guides 320 a and 320 b each can receive a line to lower fairing 314 to a desired location along structure 304, and to maintain the desired orientation of fairing 314 relative to structure 304, for example the opening of fairing 314 towards structure 304.

In operation, fairing 314 moves towards structure 304 as shown by the arrow, so that structure 304 disables member 316, and fairing 314 closes due to biasing force.

When fairing 314 closes, male member 318 a is locked within female member 318 b, as shown in FIG. 3 b.

A space may be defined between the exterior of structure 304 and the interior of fairing 314, which allows fairing 314 to weathervane with varying current directions.

One or more portions of the system may be or contain copper to retard marine growth.

Fairings may be replaced with strakes, shrouds, wake splitters, tail fairings, buoyancy modules, or other devices as are known in the art. Suitable sleeves, suitable collars, and suitable devices to install exterior to structures, and methods of their installation are disclosed in U.S. patent application Ser. No. 10/839,781, having attorney docket number TH1433; U.S. patent application Ser. No. 11/400,365, having attorney docket number TH0541; U.S. patent application Ser. No. 11/419,964, having attorney docket number TH2508; U.S. patent application Ser. No. 11/420,838, having attorney docket number TH2876; U.S. patent application Ser. No. 60/781,846 having attorney docket number TH2969; U.S. Patent Application Number 60/805,136, having attorney docket number TH1500; U.S. Patent Application Number 60/866,968, having attorney docket number TH3112; U.S. Patent Application Number 60/866,972, having attorney docket number TH3190; U.S. Pat. No. 5,410,979; U.S. Pat. No. 5,410,979; U.S. Pat. No. 5,421,413; U.S. Pat. No. 6,179,524; U.S. Pat. No. 6,223,672; U.S. Pat. No. 6,561,734; U.S. Pat. No. 6,565,287; U.S. Pat. No. 6,571,878; U.S. Pat. No. 6,685,394; U.S. Pat. No. 6,702,026; U.S. Pat. No. 7,017,666; and U.S. Pat. No. 7,070,361, which are herein incorporated by reference in their entirety.

Suitable methods for installing fairings, collars, and other devices to install exterior to structures, are disclosed in U.S. patent application Ser. No. 10/784,536, having attorney docket number TH1853.04; U.S. patent application Ser. No. 10/848,547, having attorney docket number TH2463; U.S. patent application Ser. No. 11/596,437, having attorney docket number TH2900; U.S. patent application Ser. No. 11/468,690, having attorney docket number TH2926; U.S. patent application Ser. No. 11/612,203, having attorney docket number TH2875; U.S. Patent Application Number 60/806,882, having attorney docket number TH2879; U.S. Patent Application Number 60/826,553, having attorney docket number TH2842; U.S. Pat. No. 6,695,539; U.S. Pat. No. 6,928,709; and U.S. Pat. No. 6,994,492; which are herein incorporated by reference in their entirety.

The collars and/or fairings may be installed on the connector member before or after the connector member is placed in a body of water. The collars, fairings and/or other devices exterior to the structure may have a clamshell configuration, and may be hinged with a closing mechanism opposite the hinge, for example a mechanism that can be operated with an ROV.

Collars may be placed between adjacent fairings, or between every 2 to 10 fairings. The collar may be a copper ring.

Fairings may be provided with copper plates on their ends to allow them to weathervane with adjacent fairings or collars. Fairings may be partially manufactured from copper.

A biodegradable spacer may be placed between adjacent fairings to keep them from binding and allow them to weathervane after the spacer has degraded.

Illustrative Embodiments In one embodiment, there is disclosed a system comprising a subsea structure beneath a body of water, subject to a water current; a collar exterior to the subsea structure, covering at least a portion of an outside surface of the subsea structure; an installation vessel floating on the body of water; a line connected to the collar and the installation vessel; and one or more vortex induced vibration suppression devices connected to the line, which have been lowered from the vessel to be installed on the subsea structure. In some embodiments, the subsea structure is selected from an umbilical, a tubular, a riser, and a tendon. In some embodiments, the vortex induced vibration suppression device comprises a fairing or a helical strake. In some embodiments, the line comprises at least two lines, the votex induced vibration suppression devices connected to the at least two lines. In some embodiments, the vortex induced vibration suppression devices are negatively buoyant in water. In some embodiments, the vortex induced vibration suppression devices comprise one or more shoulders adapted to interface with the collar and/or other vortex induced vibration suppression devices. In some embodiments, the system also includes a collar between two adjacent vortex induced vibration suppression devices, the collar connected to the line.

In one embodiment, there is disclosed a method, comprising installing a subsea structure in a body of water, wherein the subsea structure is subject to one or more water currents; installing a collar exterior to the subsea structure, covering at least a portion of an outside surface of the subsea structure; connecting at least one line to the collar and to a surface vessel; lowering at least one vortex induced vibration suppression device from the vessel towards the collar on the line; and installing the vortex induced vibration suppression device from the line to the exterior of the subsea structure, covering at least a portion of an outside surface of the subsea structure. In some embodiments, the method also includes installing additional collars exterior to the subsea structure, the collars adapted to retain the vortex induced vibration suppression devices in an axial location along the subsea structure. In some embodiments, the collar is installed on the subsea structure before the subsea structure is installed in the body of water. In some embodiments, the vortex induced vibration suppression device is installed on the subsea structure with a remotely operated vehicle (ROV). In some embodiments, the vortex induced vibration suppression device comprises an automatic closing mechanism. In some embodiments, the vortex induced vibration suppression device is installed by moving the device adjacent to the subsea structure to activate the automatic closing mechanism. In some embodiments, connecting at least one line to the collar and to a surface vessel comprises connecting at least two lines; and lowering at least one vortex induced vibration suppression device from the vessel towards the collar comprises lowering on the at least two lines.

Those of skill in the art will appreciate that many modifications and variations are possible in terms of the disclosed embodiments, configurations, materials and methods without departing from their spirit and scope. Accordingly, the scope of the claims appended hereafter and their functional equivalents should not be limited by particular embodiments described and illustrated herein, as these are merely exemplary in nature. 

1. A system, comprising: a subsea structure beneath a body of water, subject to a water current; an installation vessel floating on the body of water; a line connected to the subsea structure and the installation vessel; and one or more vortex induced vibration suppression devices connected to the line, which have been lowered from the vessel to be installed on the subsea structure.
 2. The system of claim 1, wherein the subsea structure is selected from an umbilical, a tubular, a riser, and a tendon.
 3. The system of claim 1, wherein the vortex induced vibration suppression device comprises a fairing or a helical strake.
 4. The system of claim 1, wherein the line comprises at least two lines, the votex induced vibration suppression devices connected to the at least two lines.
 5. The system of claim 1, wherein the vortex induced vibration suppression devices are negatively buoyant in water.
 6. The system of claim 1, wherein the vortex induced vibration suppression devices comprise one or more shoulders adapted to interface with a collar and/or other vortex induced vibration suppression devices.
 7. The system of claim 1, further comprising a spacer between two adjacent vortex induced vibration suppression devices, the spacer connected to the line.
 8. The system of claim 1, further comprising a collar exterior to the subsea structure, covering at least a portion of an outside surface of the subsea structure.
 9. The system of claim 8, wherein the line is connected to the collar and the installation vessel.
 10. A method, comprising: installing a subsea structure in a body of water, wherein the subsea structure is subject to one or more water currents; connecting at least one line to the subsea structure and to a surface vessel; lowering at least one vortex induced vibration suppression device from the vessel on the line; and installing the vortex induced vibration suppression device from the line to the exterior of the subsea structure, covering at least a portion of an outside surface of the subsea structure.
 11. The method of claim 10, further comprising: installing one or more collars exterior to the subsea structure, the collars adapted to retain the vortex induced vibration suppression devices in an axial location along the subsea structure.
 12. The method of claim 10, wherein a collar is installed on the subsea structure before the subsea structure is installed in the body of water.
 13. The method of claim 10, wherein the vortex induced vibration suppression device is installed on the subsea structure with a remotely operated vehicle (ROV).
 14. The method of claim 10, wherein the vortex induced vibration suppression device comprises an automatic closing mechanism.
 15. The method of claim 14, wherein the vortex induced vibration suppression device is installed by moving the device adjacent to the subsea structure to activate the automatic closing mechanism.
 16. The method of claim 10, wherein connecting at least one line to the collar and to a surface vessel comprises connecting at least two lines; and lowering at least one vortex induced vibration suppression device from the vessel comprises lowering on the at least two lines. 